1. Types of Reactions Chapter 21.3

2. Chemical Reactions Chemists have defined five main categories of chemical reactions: combustion, synthesis, decomposition, single displacement, and double displacement. Chemists have defined five main categories of chemical reactions: combustion, synthesis, decomposition, single displacement, and double displacement. a combustion reaction occurs when a substance reacts with oxygen to produce energy in the form of heat and light. a combustion reaction occurs when a substance reacts with oxygen to produce energy in the form of heat and light.

3. Synthesis & Decomposition In a synthesis reaction, two or more substances combine to form another substance. In a synthesis reaction, two or more substances combine to form another substance. The generalized formula for this reaction type is as follows: A + B  AB. The generalized formula for this reaction type is as follows: A + B  AB. Instead of two substances coming together to form a third, a decomposition reaction occurs when one substance breaks down, or decomposes, into two or more substances. Instead of two substances coming together to form a third, a decomposition reaction occurs when one substance breaks down, or decomposes, into two or more substances. A decomposition reaction is just the reverse of a synthesis. A decomposition reaction is just the reverse of a synthesis. The general formula for this type of reaction can be expressed as follows: AB  A + B. The general formula for this type of reaction can be expressed as follows: AB  A + B.

4. Single Displacement When one element replaces another element in a compound, it is called a single-displacement reaction. When one element replaces another element in a compound, it is called a single-displacement reaction. Single-displacement reactions are described by the general equation A + BC  AC + B. Single-displacement reactions are described by the general equation A + BC  AC + B.

5. Double Displacement In a double-displacement reaction, the positive ion of one compound replaces the positive ion of the other to form two new compounds. In a double-displacement reaction, the positive ion of one compound replaces the positive ion of the other to form two new compounds. The generalized formula for this type of reaction is as follows: AB + CD  AD + CB. The generalized formula for this type of reaction is as follows: AB + CD  AD + CB. A precipitate is an insoluble compound that comes out of solution during this type of reaction. A precipitate is an insoluble compound that comes out of solution during this type of reaction.